1. Field of the Invention
The present invention relates to an imaging lens-exchangeable image capturing apparatus and a control method therefore and, more particularly, a technique of correcting a focus state detected in an imaging lens-exchangeable image capturing apparatus to which an imaging lens exchangeably is attached and detached.
2. Description of the Related Art
In some conventional image capturing apparatuses having a main body unit to which an imaging lens is exchangeably attached and detached, each of the main body unit and imaging lens includes an MPU (Micro Processing Unit) to communicate with each other, thereby implementing a focus adjustment function. More specifically, it is possible to implement optimum focus detection for each imaging lens when the MPU in the main body unit side controls a sensor for detecting a defocus amount for focus detection, and the MPU on the imaging lens side transmits an optimum focus correction value for each imaging lens to the MPU on the main body unit.
For such an image capturing apparatus, so-called focus adjustment for automatic focus adjustment is well known. Focus adjustment is a technique of detecting the individual differences of parts used to tolerances in production or the like, storing, in advance, adjustment values for automatic focus adjustment according to the respective operation characteristics in a non-volatile memory upon shipping from a factory, and performing appropriate focus adjustment based on the adjustment, values.
On the other hand, for example, if a strong impact were to occur on the imaging lens or main body unit when the user drops it, a focus position may shift. Furthermore, if a quick return mirror or the like is arranged in the path of an optical system from the imaging lens to the sensor for detecting a defocus amount, the angle of the mirror may gradually change every time a shutter is opened and closed, and thus the detection accuracy of a defocus amount may decrease, thereby shifting the focus position.
In such a case, the user can bring the imaging lens or main body unit to a service center to adjust the adjustment values stored in the non-volatile memory. Since the locations of service centers are limited, a problem arises in terms of convenience and speediness.
There has been proposed a technique (micro adjustment) of storing, in a main body unit, a correction value which can be freely set by the user, in addition to adjustment values which are stored in a non-volatile memory upon shipping from a factory (see, for example, Japanese Patent Laid-Open No. 2001-174690). According to this technique, the user can freely set a correction value for focus adjustment and also return to the settings upon shipping from a factory.
In the technique disclosed in Japanese Patent Laid-Open No. 2001-174690, however, the user can freely set only one correction value. An image capturing apparatus, such as an exchangeable lens type single-lens reflex camera, to which a plurality of imaging lenses can be attached, therefore, cannot support all the attached imaging lenses.